1. Field of the Invention
The present invention relates generally to implantable blood filters. More particularly, the invention relates to caval filters having sonographically conspicuous features.
2. Related Art
Advances in many surgical specialties have saved the lives of many patients suffering serious illness or injury, and have improved the quality of life of countless others. However, such surgical repair of organs and tissues can disrupt the body""s plumbing, e.g., the circulatory system, sufficiently to give rise to new risks. For this reason, minimally invasive techniques have been developed, for example wherein highly specialized surgical tools are manipulated from outside a patient""s body through a catheter or tube inserted through a tiny incision or puncture and guided to a surgical site. Yet, both invasive and minimally invasive procedures disturb circulation sufficiently so that arterial plaques can become dislodged or clots can form in the bloodstream and move with the circulation with the body. Such debris, moving along with normal circulation, can become lodged in and partially or completely block vessels supplying blood and oxygen to critical organs, such as the heart, lungs and brain.
Medication is often used to reduce the likelihood of blood clot formation during and after surgery, however, post-operative thrombosis, as such blood clot formation is called, remains an important problem to be solved. Therefore, filters implantable in a patient""s body using minimally invasive techniques have been developed. By appropriately positioning such filters, dangerous blood clots can be removed from circulation and held in a safe location until they can be dissolved by medication or extracted, again using minimally invasive techniques. Thus, there has been a significant reduction in the incidence of morbidity and mortality due to post-operative embolism, which occurs when a thrombolus moves from its site of formation to block a vessel, becoming an embolus.
Conventional implantable blood filters employing a variety of geometries are known. Many are generally basket or cone shaped, in order to provide adequate clot-trapping area while permitting sufficient blood flow. Also known are filters formed of various loops of wire, including some designed to partially deform the vessel wall in which they are implanted.
Along with their many functional shapes, conventional filters may include other features. For example, peripheral loops or arms may be provided to perform a centering function so that a filter is accurately axially aligned with the vessel in which it is implanted. In order to prevent migration under the pressure induced by normal circulation, many filters have anchoring features. Such anchoring features may include sharp points, ridges, etc. Finally, conventional filters are known which have specific features for facilitating implanting and extracting using catheterization. Thus, a surgeon can select from a variety of conventional filters, to optimize one or another parameter of interest, and implant or extract that filter using minimally invasive techniques.
The minimally invasive techniques mentioned above require that a surgeon guide a catheter to a precise location within a patient""s body. The precise location within the body is visualized using conventional x-ray imaging and marked on the patient""s body with marker or using x-ray fluoroscopy during surgery. The position of the catheter or other instrument within the body is visualized using similar techniques. As is well-known, x-rays, a form of ionizing radiation, produce an image showing by variations in image density corresponding variations in transmission density indicative of the position of various anatomical structures and of the instrument introduced into the body by the surgeon. In order to improve the fluoroscopic image of soft tissues, such as blood vessels, contrast media are sometimes introduced into a vessel to be imaged. An instrument, which might otherwise be radiologically transparent, may also be given a radiopaque tip or other feature. However, exposure to ionizing radiation or contrast media is contraindicated for a significant number of patients, such as pregnant women or patients exhibiting anaphylactic reactions to contrast media.
What is desired is a filter, which is implantable, in vivo in a human blood vessel, without the problems or disadvantages noted above.
In one embodiment, the invention may be realized in a filter, implantable in a blood vessel by sonographic visualization. Such a filter may include one or more members arranged to trap blood clots without substantially interfering with normal blood flow; and an echogenic feature on at least one member, so the filter position can be determined by sonographic visualization. In such a filter, the echogenic feature may, for example, be a bead or a tube. Alternatively, the echogenic feature can simply by a textured or etched surface or a sharp edge or any other feature, surface, coating or geometry which is sonographically conspicuous. The filter may be placed with the assistance of a marker wire including a plurality of echogenic markers, whereby correct visualization in a sonogram of a true longitudinal slice along the filter axis is readily ascertainable by presence in the sonogram of each of the plurality of echogenic markers. Alternatively, the filter may include an echogenic tube through which the marker wire is threaded; correct visualization in a sonogram of a true longitudinal slice along the filter axis is further confirmed by presence in the sonogram of the tube in its entirety.
Filters embodying the invention may be characterized by several different geometries. For example, in one geometry, one or more members are arranged to define a cone-shaped basket attached to the echogenic feature at a vertex. The members may be further arranged to define a substantially coplanar flower, the echogenic feature attached thereto at a center thereof. The cone and flower geometries may be combined, being joined by an outer ring connecting a base of the cone to an outer position of the flower. The basket may be defined by substantially radially extending members or by a mesh of members extending in both radial directions and directions transverse the radial directions. Visibility using sonography of various geometries using the cone may be further enhanced by a plurality of echogenic markers substantially at a periphery of a base of the cone.
Filters embodying the invention may include other enhancements, as well. For example, the filter may include a plurality of loops at a periphery of the basket, whereby the basket is axially aligned thereby during deployment thereof. The filter may also include a plurality of echogenic markers substantially at a periphery of the filter, whereby deployment thereof can be visualized.
Alternative filter geometries can also include an expanded, slotted tube having slots along a predetermined length thereof, the slots dividing the slotted tube into the one or more members. Some of the geometries can be constructed with members composed of a material having a temperature-sensitive shape memory. In such an embodiment, the filter may have a deployed shape at human body temperature and a compact shape for implantation at a temperature other than human body temperature.
According to another aspect of the invention, there is a method of implanting a blood filter in a blood vessel, comprising steps of: moving a blood filter having an echogenic feature through the blood vessel to an implantation site in the blood vessel; and during the step of moving, visualizing the echogenic feature of the filter and the implantation site sonographically. Adjusting a sonographic transducer to correctly visualize in a sonogram a true longitudinal slice along the filter axis, which is readily ascertainable, may enhance this method by presence in the sonogram of at least one echogenic feature of the filter.
According to yet another aspect of the invention, a caval filter placement set includes a guide wire, a dilator, a sheath for introducing the filter, a caval filter including one or more members arranged to trap blood clots without substantially interfering with normal blood flow, and an echogenic feature on the caval filter, so the filter position can be determined by sonographic visualization. Moreover, the guide wire may be bent to facilitate locating a renal vein.
These and other features, objects and advantages of the invention will become apparent upon reading the following detailed description of some embodiments thereof, in connection with the drawings.